In the drug development field, there is a case where an influence of a medicine administered to a sample such as a myocardial cell is evaluated on the basis of light emitted from the sample. Patent Literature 1 discloses a light measurement device capable of improving measurement sensitivity to light coming from a sample. In this device, in a measurement region set corresponding to a well on a light detection image, a two-dimensional luminance value distribution within the measurement region and a predetermined luminance value threshold value are compared so as to extract from a measurement region an analysis region on which analysis processing is to be performed. Analysis processing is performed by using data of the luminance value within the analysis region as analysis data.